Objectives. The objectives are obtain the internal consistency, validity and factorial structure of the Self-Efficacy for AIDS scale, wich was developed in American population by Kasen, Vaughan and Walter (1992) and adapted in mexican samples for López and Padilla (1999). Instruments: It is employed the Self-efficacy to Prevent the AIDS Scale of 27 items of López and Padilla (1999), together with closed questions Likert type, dicotomics and two opened questions on relevant aspects of the sexual conduct to validate the scale, under a format self-applied test of pencil and paper. Material and Methods. It is a correlacional study with a not experimental design of transverse type. It was accomplished with a simple random sample of 962 adolescents wich were taken of 60 public health centers of Monterrey. None went to consult by motives related to the AIDS. Results. The scale was adjusted to a normal distribution (Zk-s(Normal)=1.369; p=0.047). It presents a mean of 95.14 and a standard deviation of 25.80. Its reliability, by the alpha of Cronbach, was 0.89. SEA - 27 shows a structure of four independent factors that explain 58.47% of the total variance. Conclusions: Thus, it is concluded that SEA - 27 is a reliable and valid scale. The English version of this paper is available at: http://www.insp.mx/salud/index.html